1. Field of the Invention
The present invention generally relates to mat members and exhaust gas processing apparatuses, and more particularly to a mat member which includes inorganic fiber and an exhaust gas processing apparatus which includes such a mat member and is suited for use in vehicles and the like.
2. Description of the Related Art
The number of automobiles has increased considerably in this century, and the amount of exhaust gas emitted from internal combustion engines of the automobiles has shown a sharp increase. Particularly, various materials included within the exhaust gas of a diesel engine cause air pollution which greatly affect the environment on a world wide basis.
Under such circumstances, various exhaust gas processing apparatuses have been proposed and reduced to practice. A general exhaust gas processing apparatus has a tubular casing provided at an intermediate portion of an exhaust pipe that connects to an exhaust manifold of the engine, and an exhaust gas processing body accommodated within the tubular casing. The exhaust gas processing body has a inlet and an outlet for the exhaust gas, and a large number of micropores are provided within the exhaust gas processing body. Examples of the exhaust gas processing body include catalyst carriers, and exhaust gas filters such as Diesel Particulate Filters (DPFs). In the case of the DPF, for example, when the exhaust gas enters from the inlet of the exhaust gas processing body and exits from the outlet of the exhaust gas processing body within the casing, particles are trapped on walls surrounding the micropores to thereby remove the particles from the exhaust gas.
Normally, a holding seal member is provided between the exhaust gas processing body and the casing. The holding seal member prevents damage caused by the contact between the exhaust gas processing body and the casing when the vehicle or the like moves, and prevents the exhaust gas from leaking from a gap between the casing and the exhaust gas processing body. In addition, the holding seal member also prevents the exhaust gas processing body from falling off from the casing due to the exhaust gas pressure. On the other hand, the exhaust gas processing body is required to maintain a relatively high temperature in order to maintain its reaction, and the holding seal member is required to be heat resistant. In order to satisfy these requirements, the holding seal member may be made of a mat member which includes inorganic fiber such as alumina fiber.
The mat member is wound on at least a portion of an outer peripheral surface of the exhaust gas processing body, excluding the inlet and outlet, and is integrally fixed to the exhaust gas processing body by taping or the like in order to function as the holding seal member. Thereafter, the exhaust gas processing body, having the mat member integrally fixed thereon as the holding seal member, is press-fit within the casing to form the exhaust gas processing apparatus.
In the conventional exhaust gas processing apparatus, it is known from experience that the holding force of the holding seal member with respect to the exhaust gas processing body decreases in a relatively high temperature region of 400° C. to 500° C. In addition, when the holding force of the holding seal member with respect to the exhaust gas processing body greatly decreases, the exhaust gas processing body may fall off from the casing. In order to suppress the decrease in the holding force of the holding seal member with respect to the exhaust gas processing body in the high temperature region, the use of a mat member added with a material (or agent) that swells (or expands) as a result of heat exposure, such as vermiculite, which expands in the high temperature region, has been proposed in a Japanese Laid-Open Patent Publication No. 11-509287, for example.